GLANDS. 



[ 291 ] 



GLEICHENIE.E. 



Simple external glands are either sessile 

 vesicles or hairs, composed of a single vesi- 

 cular or elongated epidermal cell filled with 

 secretion ; or they are hairs composed of a 

 simple row of cells, one or more of which 

 are filled with secretion. Examples of this 

 may be found in the epidermis of Primula 

 sinensis, Gilia tricolor, Erodium cicutarium, 

 Achimenes (PI. 21. fig. 32), Stachys, Marru- 

 bium, Digitalis purpurea (PL 21. fig. 33), 

 Antirrhinum majus (P1.21 . fig. 34), (Enothera, 

 Helleborus fcetidus, Scrophularia nodosa, 

 (PL 21. fig. 41), Sempervivum, Salvia, Thy- 

 mus, Melissa, Mesembryanthemum, Garden 

 Chrysanthemum (PL 21. fig. 30), &c. 



The stings of the nettles are to be placed 

 here ; they consist of very long, tapering, 

 single hairs, with an obtuse point, and a bulb- 

 like expansion at the base imbedded in a 

 dense layer of epidermal tissue (PL 21. fig. 

 8). The hair is filled with the poisonous 

 secretion. When the point touches the skin, 

 it breaks off and allows the escape of the 

 fluid contents, which are squeezed out by 

 the pressure, and probably by the tension of 

 the tissue around the bulb. 



Compound external glands differ from the 

 simple only in the fact that they are com- 

 posed of a greater or smaller number of cells 

 combined into a mass, usually of spherical 

 or allied form. They may be sessile, or 

 stalked upon a simple or compound hair. 

 Examples of sessile form occur in Dictamnus 

 albus (PL 21. figs. 38, 39), Robinia viscosa, 

 the leaf of the Mulberry and the HOP (PL 21 . 

 fig. 14), and the stipular glands of Cinchona, 

 Galium, &c. ; of the stalked, in the Rose 

 (PL 21. fig. 46), species of Rubus, Drosera, 

 and on many aromatic or viscid plants. 



Internal glands. These consist of cavities 

 in the sub-epidermal tissue, of variable size, 

 bounded by a firm layer of cells, and filled 

 with oily or resinous "secretions. They ap- 

 pear to be formed either of one cell, when 

 small, or, when large, of a definite mass of 

 cells, which, after the production of the se- 

 cretion, have their walls obliterated so as to 

 form a large chamber; possibly, however, 

 they may be intercellular spaces into which 

 the secretion is poured out. Examples of 

 moderate dimensions are found in the leaves 

 of Dictamnus, Magnolia (PL 21. fig. 12), 

 Hypericum perforatum, and other species, 

 Myrtacece, Ruta graveolens (PL 21. fig. 11), 

 &c. Very large glands of this kind contain 

 the oil in the rind of the orange (fig. 284) 

 and other species of Citrus. 



The nectaries of flowers have their tissue 



metamorphosed into a condition resembling 

 that of the secreting part of glands, and the 

 hairs of the stigma of Flowering Plants pro- 



Section of the rind of an orange, showing the internal 

 glands, R, KI 



Magn. 50 diams. 



duce a secretion at the period of impregna- 

 tion. Brongniart has lately pointed out the 

 existence of internal glands in the dissepi- 

 ments of the ovaries of the petaloid Mono- 

 cotyledons. These structures form a trans- 

 ition to the turpentine-canals, &c. of the 

 Coniferae. (See SECRETING ORGANS, of 

 Plants). The gummi-keulen of Meyen (cysto- 

 lithes of Weddell) are also related to glands. 

 (See RAPHIDES.) 



BIBL. Meyen, Secretionsorgane der Pflan- 

 zen. Berlin, 1837; Manuals of Vegetable Ana- 

 tomy; Brongniart, Ann. des Sc. nat. 4 ser. 

 ii. p. 5 ; Lawson, Ann. Nat, Hist. 2 ser. xiv. 

 p. 161. 



GLAUCOMA, Ehr. A genus of Infuso- 

 ria, of the family Trachelina, E. 



Char. Body ciliated all over ; mouth lon- 

 gitudinal, oval, without teeth, placed late- 

 rally near the anterior third or fourth of the 

 body, and furnished with one or two tremu- 

 lous laminae or lips. 



Stein describes the encysting process as 

 occurring hi one species. 



G. scintillans, E. (PL 24. fig. 8). Body 

 colourless, slightly depressed, elliptical or 

 ovate; sacculi large ; length 1-290''. Aqua- 

 tic, and in infusions (of hay, &c.). 



G. viridis, D. Body green, oval ; mouth 

 large, nearer the middle than the anterior 

 end of the body; length 1-630". In putrid 

 rain-water collected in an empty wine-cask 

 coated with cream of tartar. 



BIBL. Ehrenb. In/us, p. 334 ; Dujardin, 

 Infus. 475 ; Stein, In/us. 250. 



GLEICHENIE.E. A tribe of Polypodia- 

 ceous Ferns, distinguished by then* obliquely 

 annulated sporangia arranged in fours (fig. 

 286). Genera : 



I. GLEICHENIA. Sporangia collected in 

 roundish sori. Indusium absent. Leaves 

 forking. Exotic (figs. 285 & 286). 



